High-temperature casting investment



Patented July 2, 1929. V

UNITED STATES 1,719,276 PATENT oFF cE.

' CHARLES A. OVEBIIRE, OF SAN FRANCISCO, CALIFORNIA A SBIGNOR TOIHE WESTERN GOLD & PLATINUM WORKS, OF SAN FRANCISCO, CALIFORNIA, A GORPOBATIOR O! oarmonu'm.

Ho Drawing.

My present invention relates to an improved investment, and more particularly, to a mixture for forming investments such as are used by dentists and jewelers which is particularly adapted for use in cast ng metals and alloys having a high melting point. I

An object of my invention isto provide a mixture in powdered form which, when .10 combined with water, can be used to form an investment of the type used by dentists and jewelers which will stand a high degree of temperature without disintegration.

Another object of my invention is to pro- 1 vide a powdered mixture which, when mixed 3 as I have been able to determine, are comprised principally of plaster of Paris and sand of different degrees of coarseness. These materials work very satisfactorilyin the melting of gold and its alloys which melt at a relatively low temperature. However, where it isdesired to cast metals, such as platinum, palladium, and their alloys, having relatively high melting points, the above materials are wholly unsatlsfactory as they disintegrate at temperatures below which these lattermetals and alloys melt and it is therefore a further object of my invention to provide an investment in which the above metals and alloys may be melted and cast.

I have discovered that it is ossible to construct an investmenthaving a 1 the desirable characteristics of the investments formed by the presentexisting commercial mixtures with the additional'advantage that it will stand up under the high temperatures such. as are required in melting the above referred to metals. The materials which I propose to incorporate in my mixture are magnesium oxide plus a suflicient quantityof calcium sulphate to effect a proper binding of the materials. The magnesium oxide should be of a suitable fineness which will be dependent upon the smoothness of the invest- Applieatlon filed Kay 28,

lyfbeen placed and there allowed to harden.

nIGH-TEMPEBATURE CASTING INVESTMENT.

192s. Se'rlal'lio, 280,118.

'limit myself to these proportions, as it is possible to produce suitable investments for various different classes of'work with different proportions of the above ingredients. The proportions set forth above are thought by me to be the most suitable for all-around work. In my experiments I have found that fused magnesium oxide, because of its. greater purity and non-shrinkin characterlstics, is particularly suited to t is use. It should be understood, however, that ordinary commercial magnesiumoxide can be used with good results. a

In the particular branch of the art to which my invention appertains, it is customary to melt the metal to the molten state on the outer surface of the investment and then force the molten metal through a small sprue -or gate and 'into the impression formed therein. Investments such as are contemplated b my invention are formed as follows A ter mixing the above ingredients in the proportions set forth above or other proportions, if desired, the same will be mlxed with enough water so that the mixture will just pour. This mixture is then poured into.

a flask within which a pattern has previouster the investment has hardened sufiicienty to withstand handling within the flask it will be heated to drive out the remaining water. The pattern, which is of a meltable material such as wax, will then be melted out of the investment and the pattern holding pin withdrawn to form the s rue or ate thrpugh which the metal to be ater me ted can be'forced into the impression. After the above operations, the investment will be placed in the casting machine and the metal brought to the molten state under the action of a blo-wpipe or acetylene torch and then forced into the mold.

After the casting operation has been carried out, the investment, to ether with its flask and enclosed casting w en submerged in water, will completely disinte rate and crumble away from the casting, caving it clean and bri ht. This latter feature constitutes a fart er advantage in addition to itshigh temperature characteristics, as it makes theproblem ofremoving the casting less diflicult than when ordinary present-day materials having much lower temperature characteristics are used. a 7

While I have described a preferred embodiment of m invention as now known to me, it 'is to e understood that various changes may be made therein without devparting from the spirit of the invention as defined in the a pended claims. 7

Having thus described my invention, what I claim and desire to secure by Letters Patent is- 1. A mixture for forming investments suitable for the casting of high melting point metals and allo s composed of at least 50% magnesium-oxi e and the remainder calcium sulphate.

2. A mixture for forming investments suitable for the casting of high melting point metals and alloys composed of substantially 75% magnesium oxide and 25% calcium sulphate by Weight.

3. A mixture for forming investments suitable for the casting of high melting point metals and alloys containing not less than 50% fused magnesium oxide and the remainder calcium sulphate.

4. A mixture for forming investments suitable for the casting of high melting point metals and alloys containin from 50% to 90% magnesium oxide an respectively, fromv50% to 10% calcium sulphate.

5. An investment for melting and casting platinum and its alloys composed of not less than 50% magnesium oxide with calcium sulphate as a binder.

6. An investment for melting and casting high temperature metals and alloys composed of not less than 50% fused magnesium oxide and the remainder a suitable binder.

CHARLES A. OVERMIREV 

